MobArena error

00:15:42 [SEVERE] null
org.bukkit.command.CommandException: Unhandled exception executing command 'ma'
in plugin MobArena v0.94.4.47
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:42)
        at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:16
8)
        at org.bukkit.craftbukkit.CraftServer.dispatchCommand(CraftServer.java:3
82)
        at net.minecraft.server.NetServerHandler.handleCommand(NetServerHandler.
java:768)
        at net.minecraft.server.NetServerHandler.chat(NetServerHandler.java:728)

        at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:721)
        at net.minecraft.server.Packet3Chat.a(Packet3Chat.java:33)
        at net.minecraft.server.NetworkManager.b(NetworkManager.java:226)
        at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:96)
        at net.minecraft.server.NetworkListenThread.a(SourceFile:108)
        at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:534)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:432)
        at net.minecraft.server.ThreadServerApplication.run(SourceFile:465)
Caused by: java.lang.NoClassDefFoundError: Could not initialize class com.garbag
emule.MobArena.events.ArenaPlayerJoinEvent
        at com.garbagemule.MobArena.ArenaStandard.playerJoin(ArenaStandard.java:
519)
        at com.garbagemule.MobArena.commands.user.JoinCommand.execute(JoinComman
d.java:63)
        at com.garbagemule.MobArena.commands.CommandHandler.onCommand(CommandHan
dler.java:87)
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:40)
        ... 12 more
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